In general, a boat is provided with an engine which is designed about an axis to bring the engine inwardly or push it outwardly from the boat to change the trim or, thrust angle of the propeller force between an upwardly inclined angle and a downwardly inclined angle. When the operator adjusts the throttle for greater speed, he must then retrim the outboard or inboard/outboard engine for optimum performance. When the throttle is readjusted for low speed, the trim must be readjusted. The operator must depress the tilt switch and visually monitor engine position.
Recently, it has been desirable to provide an automatic trim adjustment assembly which automatically adjusts the trim of the engine or drive unit, depending upon the speed of the boat. One such assembly is disclosed in U.S. Pat. No. 4,718,872, issued Jan. 12, 1988 in the name of Olson et al which discloses an automatic trim system that automatically senses for increase and decrease in speed. The system will step the trim motor and determine whether the speed of the boat has increased. If the speed of the boat decreases due to the new position of the engine, the trim motor will return the engine to the previous position where the boat has maximized its speed. Other types of systems disclose trimming a boat based on the angular position of the boat with respect to the water and the tilting thereof, which is disclosed in U.S. Pat. No. 4,401,888 in name of West et al and U.S. Pat. No. 4,524,710 in the name of Scott.
The problem with these types of assemblies is that continuous change of the trim is not necessary, and manual change in the trim at predetermined speeds may be desired with return to predetermined positions at predetermined speeds.